Bug 33845: Headings become cursive in TOC when they contain an image

Bug 33845: Headings become cursive in TOC when they contain an image
Fixes the problems with r102179 and r102179, as there are
valid tags which begin the same, which meant they were not removed from
the TOC (the second regex, intended to remove tag parameters, then converted
<img or <blockquote> into <i> / <b>).
The same problem existed in the original regex, but as there are no valid
tags which begin with sup or sub, it never happened).

Added comment explaining the tocline regex, and added a bunch of parser tests.